A beam guiding device is typically embodied for beam guidance of a laser beam, e.g., a CO2 laser beam, with a very high power (>10 kW). By way of example, the beam guiding device can be integrated into an EUV radiation generating apparatus to guide the laser beam in a direction of a target region for generating EUV radiation, the laser beam being focused on said target region with high accuracy. Another application for a beam guiding device for guiding a laser beam with a very high power (>10 kW) is represented by a laser processing machine which, for example, can be employed in welding applications.
A beam guiding device for an EUV radiation generating apparatus with a device for increasing the beam diameter (beam widening), which includes two off-axis parabolic mirrors in one exemplary embodiment disclosed in US 2011/0140008 A1. The beam guiding device described therein serves to guide laser radiation which was produced and amplified in a beam generating device in the form of a driver laser system. The beam guiding device guides the laser beam from the driver laser system to a focusing element or to a focusing device which serves to focus the laser beam into a target region in which a target material is provided, said target material transitioning into a plasma state upon irradiation with the laser beam and, in the process, emitting EUV radiation.
WO 2014/048563 A1 describes a beam guiding device for an EUV radiation generating apparatus, including a device for increasing or reducing the beam diameter of the laser beam. The device includes a first off-axis paraboloid mirror with a first, convexly curved reflecting surface and a second off-axis paraboloid mirror with a concavely curved reflecting surface. The beam guiding device includes a movement device which is embodied to modify a distance between the first reflecting surface and the second reflecting surface for modifying the aperture angle of the laser beam. When the distance is modified, there is not only a change in the aperture angle of the laser beam but also a (minor) change in the beam diameter.
A laser beam emitted by a beam generating device in the form of a laser source may vary both in respect of the beam diameter and in respect of the aperture angle (e.g., the beam divergence/beam convergence), depending on the emitted power of the laser source. Even in the case of laser sources with the same construction, the emitted laser beam may possibly vary from specimen to specimen, both in respect of the beam diameter and in respect of the aperture angle, in the case of identical operating parameters.